


Sex Ed With Lust

by Krystal_Twi



Category: Undertale (Video Game)
Genre: Background Poly, Basically random slice of life oneshots with sex ed lessons, Dildos, Ecto-Genitalia (Undertale), Ecto-Tongue (Undertale), Lustberry, M/M, Please do your own research. I am no expert and sexual health is no joke, STDs, STI, Sex Education, Sex Shops, Sex Toys, Sex ed but with Lust, as sfw as this can get
Language: English
Status: In-Progress
Published: 2019-03-31
Updated: 2019-04-02
Packaged: 2019-12-29 00:56:38
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 2,577
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18297164
Author URL: https://archiveofourown.org/users/Krystal_Twi/pseuds/Krystal_Twi
Summary: You know what I want? A sex ed fic or comic with Lust!Sans teaching sex ed to all the other Sanses and Papyruses.Having Lust and another Sans in a sex shop and one Sans goes straight to something that has Lust mentally freaking out and going on about the reasons why it was a bad thing and leading the other Sans to something better suited for them.Or one Sans doing something that can cause an sti (sti’s can be caused through non-sexual means) and Lust going on a lecture on that and giving the Sans advice for the future.Lust being the best sex ed teacher in the multiverse.  So I did it.Follow this series as Lust teaches his friends and boyfriends in their everyday life about sexual health and more.





	1. Chapter 1

**Author's Note:**

> We all needed better sex ed. But they refused to teach us. Shame. 
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> Twitter

Blue shifted on his feet. His fingers tapping away at his pants leg. Nerves shooting through him as he could swear on his soul that the cashier was watching him. He wasn’t exactly in his comfort zone and he knew it showed brightly.

 

He could hear Lust, his boyfriend, faintly in the background making excited chirping noises as he pranced around the store. He regretted telling Lust he never used a sex toy before. His lavender colored boyfriend was having way too much fun, running around the store like a kid in a candy shop.

 

Blue sighed, bringing a hand up to his neck. Giving the bone there a stressed rub as he closed his eyesockets. Lust asked him and it wasn’t like he couldn’t have said ‘no’. Lust had asked multiple times if he was sure about going. But Blue had a hard time telling his datemates (yes, more than one) ‘no’ to anything.

 

Even if it meant being at a sex store.

 

A hand landed on his shoulder. Blue nearly jumped from his boots, head snapping back to see bright lavender heart eyelights. “You okay, Précieux?” Lust asked, a kind smile on his face. His eyelights flickering to the large shelves of sex toys. “Having trouble picking?”

 

Blue blushed, swallowing and looking away. “Something like that,” Blue mumbled, his voice low as he looked to the ground.

  
“Mon amour, take your time,” Lust tried to reassure. Smiling at Blue, grabbing him by his chin and kissing his cheeks. Blue’s soul glowed from the kiss. “How about we go and check around the rest of the store some more?”

 

Blue gave his boyfriend a smile. “Okay,”

 

Lust grabbed his hand, leading him away from the front of the store and towards the back. Blue may feel like a fish out of water, he had his boyfriend. Blue kept pace with his excited datemate.

 

When they got to the last aisle, Lust squeezed his hand. Lust tilted his head to the aisle, encouraging Blue to go and have a look. Blue squeezed his boyfriend’s hand in return. His eyelights going to the aisle and searching from his spot.

 

Blue’s eyelights snapped into hearts when he caught sight of a toy in the middle of the aisle. His soul thumping wilding as he lost his breathing.

 

It was a bright, glowing red dildo. It wasn’t long at all. Maybe six inches at more but it made up for it in thickness. It was thick at the top but slowly became thinner near the bottom. Small spikes decorating the toy around the tip. It made all the extract magic in Blue’s mouth evaporate.

 

Stars…

 

Blue swallowed, walking towards the bright, red, dildo. His fingers flexing and bending at his side. Blue raised his hand out to go and grabbed the toy, but a hand carefully grabbing his own. Stopping him from reaching his prize.

 

Lust lowered Blue’s hand, giving the other a smile. “I personally wouldn’t pick that one, Baby Blue,” Lust purred, raising his arm to lean onto Blue. Smiling a Cheshire cat at Blue but there was concern in his eyelights.

 

“Why not?” The heart eyes in Blue’s eyesockets faltering. A look of hesitance flashing on his face.

 

“Its a jelly based,” When he got a confused look from Blue, Lust elaborated.“The jelly based toys are usually filled with harmful chemicals,” Lust waved his hands in a small motion, trying to make his point. “It’s not exactly safe for _personal_ use,”

 

Blue stared at his boyfriend in confusion. His eyesockets blinking as his eyelights flickered to the toy and to Lust. “What do you mean?”

 

“There are a lot of negative side effects the wrong type of material can cause, some side effects even being long lasting.” Lust shrugged his shoulders, looking over his shoulder while placing a hand on his hip. “Jelly based ones, in general, have been said to cause: Headaches, nausea, cramps, and etc,”

 

Lust went on ranting, seeming getting lost in his own little lecture. Crossing his arms as he went. “They also have phthalates in them. Phthalates help the toys be flexible, but they are **not** good for any sexual use. There have been studies of them harming organs and causing cancer.”

 

Lust looked up, his fingertips tapping at his arm. “And that’s only the jelly based toys. There are **tons** of more toys made from different toxic, and nontoxic, materials that have been known to harm our bodies,”

 

Blue frowned, eyebrow bones furrowing in confusion. “If it's that bad, why is it used in sex toys?” Lust sighed, shrugged his shoulders, a frown on his face.

 

“Unfortunately, there is no guideline on what can or cannot be used in sex toys,” Lust shook his head. “There is some stuff that is not even allowed to be in dog toys but can be found in sex toys,” Lust than sighed, annoyance fluttering in his eyelights as he grumbled. “Some companies even resort to changing the name of their jelly toys so the toy itself would appear safer,”

 

Blue’s eyesockets widen. Staring at his boyfriend in shock. “Is that even legal?” Blue couldn’t understand how it could be. Wouldn’t that be fraud? Plus, doesn’t it scream something if something is unsafe enough to make you consider tricking people?

 

Lust tilted his head to the side, disappointment in his eyelights. “Companies are using a loophole to get away with it. Labeling sex toys as novelty items, which unlike other stuff aren’t subjected to mandated testing. Letting them give short, simple labels to their products.”

 

Lust reached over and grabbed the sex toy that Blue had been eyeing. Carefully tossing the toy to Blue. “If you do get it, please use condoms with it,” Lust turned his head, searching for the condoms. “Even then, you have to be extremely careful. Some condoms can breakdown due to certain oils and lube or just be faulty,” Lust shrugged his shoulders.

 

Blue stared at the toy with denouncement. He looked up at his boyfriend, pouting at the new revelations brought to light to him. “Are there any safe materials?” Blue asked cautiously.

 

Lust’s expression changed. Lust nodded his head, a bright smile on his face. He turned his head, looking for something. His eyelights blazed brightly once landing on something. Lust ran down the aisle, grabbing a few packages and running back.

 

In his hand were: a glass dildo, bumpy and rather short, a heart handle on the end. A blue toy that was long, thick and curved with a few buttons on the bottom. The last looked to be a pure metal anal plug with a ruby heart handle. The excitement in Lust’s eyes looked giddy as he took a breath and began to rant once more.

 

“The best is the non-porous body safe materials!” Lust started,  basically juggling the packaged toys in his grasp.“Most of the safest toys to use are glass, stainless steel, hard plastic, 100% pure medical-grade silicone, metal, _hell_ even wood!” Lust had a look of excitement as he juggled the toys in his arms.

 

“It’s all about picking the right toy and material that you like the most.” Lust tried his best to point at Blue with his finger, despite his arms being full. “We can get one type of material and see if you like it. If you don’t, no harm in trying out some different ones,”

 

In the end, Blue was able to pick out a short, thick dildo made from silicone. _(Fortunately, there were spikes. Not as thick as the jelly spikes but the spikes ran all over the dildo)_. Along with water-based lube that Lust insisted on getting. Something about water-based lube doesn’t break down the silicone in the toy while other lubes could.

 

Either way, Blue ended up having a _good_ time.

 

**Notes for the Chapter:**

> **Also don't use any toy with the word "Skin" or "Flesh" in the name. Be cautious of those as well!**
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>  Tada... Idk. I'm leaving the links to resources I used to help anyone who wants to do further research on each chapter issue. 
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>  Also, I live for Lust giving his datemate's pet names from other languages. Blue's in general is Precious or my love in french.
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>  **Resource one**  
>  https://sluttygirlproblems.com/guide/dangers-jelly-sex-toys/ 
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> **resource two**  
>  http://dangerouslilly.com/toxictoys/
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>  **resource three**  
>  http://dangerouslilly.com/2010/07/ask-lilly-how-do-i-know-if-a-sex-toy-has-phthalates-in-it/
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>  **resource four**  
>  https://www.dailymail.co.uk/femail/article-4381166/Why-sex-toys-exposing-people-harmful-chemicals.html
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> I apologize, orignal links weren't working, so i will be using original urls from now on.


	2. The importance of Regular sti/std test

**Summary for the Chapter:**

> Red and Lust have a talk about the importance of regular sti/std test done and why

**Notes for the Chapter:**

> OKay, STI’s and STD’s are basically the same things… STI is the infection and the STD is the disease, what happens when the sti isn’t treated… BUT STI doesn’t always mean you got an STD. Confusing? For me it is. XD
> 
> it’s hard to explain, so I encourage people to search it themselves to understand it better.  
>  _Difference between STI's and STD's link_  
>  https://beforeplay.org/the-difference-between-stds-and-stis/

Lust hummed a happy tune under his breath as he picked up his shoes near the door. It was nearing two o’clock and he needed to hurry if he wanted to catch a bus. He wanted some fresh air and doctors orders were to not teleport before an appointment. Teleporting did drain his magic and if teleported, it would be hard to know for sure if it was an illness or STI that caused the drainage of magic or not.

 

Yes, he was heading to the doctors for a few STI tests to be run. He always made sure to go and get some done every few months. Best to be sure than to be in dangerous waters.

 

Lust made his way to the couch. He flopped down on the overly cushioned furniture, planting a foot on the table in front of him. He put his shoes on, which for once wasn’t slippers. Dark purple tennis shoes with mint blue laces. He may not be a fashion icon but he knew how to match his clothing.

 

“Where ya off too?” Lust looked up from where he was tying his shoes. His eyelights locked on crimson ones. Red. Red was another one of Lust’s boyfriends. One he shared with Blue. Red was Lust’s teddy bear. His cuddly, spiky teddy bear.

 

Lust gave Red a bright smile. “Heading off to my doctor to get tested,” Lust explained with ease. It didn’t bother him if his boyfriend knew of him going to get STI/STD test done. If he did have something, he would have to tell them all anyways.

 

Red looked confused. “Why? We all wear condoms, even if we didn’t it’s not like we could catch something if we are all clean,” Lust frowned, head tilting to the side.

  
  
“How do you know we are all clean?” Lust asked, lowering his foot from the table. His eyelights never leaving his teddy bear enchanting crimson ones. Lust was curious about how sure Red could be about all of them being clean.

  
  
Red shrugged his shoulders. Looking at the five random socks that laid in the corner. “We got tested a few times before, none of us ever got anything. Why would we have it now?”

 

“There is no guarantee that we stayed clean though,” Lust frowning at his boyfriend. “We can easily catch an STI and then pass it along to one another,”

 

“What do you mean? None of us brought in a new partner in a year now,” Red asked confused. The last partner to be introduced to their poly relationship was Razz, the cute little tsundere. “And Razz had been clean,” Lust gave Red a smile.

 

Lust put on his next shoe, quickly tying the laces so he could get back to his conversation. “ _Had_  been. He could have caught something since then,”

 

“How? He hasn’t had any new partner to get anything from,” Red was quick to point out. Which was true, Razz wasn’t seeing anyone knew and normally only kept affection to his two datemates, Red and Blue.

 

“Red, there are STI's that can be caught through nonsexual means,” Lust informed, blinking up at his edgy boyfriend. “Just cause it is labeled as sexually transmitted, doesn’t mean that’s the only way to catch it,”

 

Red frowned, only the tip of his gold tooth showing. “What? You’re kidding right?” Lust shook his head. Lust scooted back on the couch, getting comfortable as he would be here longer than he thought. Not that it was a bad thing, this stuff needed to be talked about.

 

“Hepatitis A can be caused through contaminated food,” Lust began listing off, “UTI’s can be caused by thongs or sitting around in damp clothing, Crabs can be transmitted through the touch of hair that has been contaminated, scabies can be caused by just sharing bedding with an infected person, Herpes by sharing silverware, and those are just one or two ways to catch them,”  

 

Lust shrugged his shoulders, hands going up in a ‘ _whatcha going to do?’_ motion. “There are other non-sexual ways to catch any one of these STI’s or more STI’s that I didn’t even mention. It’s just more common to get them sexually,”

 

Red at this point looked slightly horrified. “That is a lot,” Lust nodded his head, a pout on his skull. Red shut his eyesockets, shaking his head. “Even so, we haven’t caught it. We would have known,”

 

Lust winced mentally, biting the tip of his finger. “Actually…” Red stared at his boyfriend, part of him worried about what the purple skeleton would say. “Some STIs and STDs _can_ be asymptomatic,”

 

When Red raised an eyebrow in confusion, Lust was more than happy to explain. “You can have it and not have any symptoms.” Lust elaborated. “Herpes, once again, is an example of this. In fact. Most people who get it, don’t even know until there is an outbreak! Which can be years after getting it, even though it’s more common to get them in the first few weeks.”

 

Lust did his best ‘duck face’ as he could, seeing he was a skeleton as he sat there in thought. “Chlamydia is another STI that most people don’t know they have. Around 75% of females who have it, don’t experience symptoms and 50% of males don’t either,”  Lust continued.

 

It took a minute for Red to process the additional information. To have an STI and not even know it sounded worrying. How many people have gotten one because someone thought they were clean?

 

Red swallowed the growing magic in his mouth, letting out a nervous laugh. “I guess it’s a good thing we have safe sex then, huh?” Red asked as he made his way to sit next Lust, lacing their fingers together. Red really needed to learn to not jinx himself.

 

“There is no such thing as _‘safe’_ sex, only _safer_ sex,” Lust laid his head on his boyfriend’s shoulder, focusing on where their hands were intertwined. “Condoms are used for protection, but at the end of the day they don’t prevent all STI's.”

 

Red froze, his eyelights staring at his boyfriend’s skull. “Please tell me you’re jokin’…” Lust shook his head. His lavender eyelights going to the clock on the wall. His appointment was close. Maybe he should cancel and make more appointments next week for all of them.

 

“I wish,” Lust rolled his eyelights. “Unfortunately, no. Genital warts, herpes, crabs, syphilis are all STI's that can be spread even when using a condom. A condom does lower the risk but not always,” Lust shifted his legs. Lust lifted his head off of Red’s shoulder. “Sometimes, just skin to skin contact is enough to spread it. Or in our case, bone to bone,”

 

Lust looked off to the side, his thumb rubbing the back of Red’s hand. “So herpes alone can be spread with wearing condoms, caught through nonsexual means, and you can have it and have no symptoms. Plus, there is no cure for it,” Lust turned back to Red, giving his boyfriend a small smile. “There are more STI’s like that. Which is why we all need to get tested soon,”

 

Lust let his boyfriend’s hand and reached for his phone. Eyelights flickering to Red. “I can make you an appointment if you want,” Lust offered, already texting his other boyfriends to see if they would be willing to have a test done. “We can all make an appointment and go to Grillby’s afterward,”

 

Red didn’t need to think twice over the offer. “Yeah, I’d appreciate it, Sweetheart,” Lust gave his boyfriend a smile, leaning in and kissing his cheek.

**Notes for the Chapter:**

> This is something most of you already know, but this is important so...yeah. Yes, Red didn't know but he had to for the sake of the lesson. I feel like I explained this in a shitty way...IDK 
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> Also, I don't mean to scare anyone. Remember Lust is part of a rather big poly relationship so the risk of catching an STI is higher for them. 
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> Okay, this is an important thing to look into yourself. If you are sexually active, it's always best to go and get a test done. Even if you are using condoms. 
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> **especially if you have one night stands. There is a group of people who get off on giving other people STD's. I AM NOT JOKING. Be careful and bring your own condoms.**
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> I don't claim to be an expert so I heavily insist on doing your own research. I will be leaving my resource links. 
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> **Nonsexually transmissions info links**  
>  _one_  
>  http://www.soc.ucsb.edu/sexinfo/article/non-sexual-transmission-stis  
>  _two_  
>  https://www.stdcheck.com/blog/how-to-get-an-std-without-having-sex/  
>  _three_  
>  https://www.hivplusmag.com/wellness/2016/8/24/yes-you-can-get-sexually-transmitted-infection-without-having-sex#article-content  
>  _four_  
>  https://www.quora.com/What-are-some-STDs-that-can-be-transmitted-though-non-sexual-activities  
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> **Links to Condoms/STI's that condoms can't prevent**  
>  _one_  
>  https://www.getthefacts.health.wa.gov.au/faqs/do-condoms-protect-against-all-stis   
> _two_  
>  https://health.williams.edu/medical-diagnoses/sexual-and-reproductive-health/male-latex-condoms-and-sexually-transmitted-diseases/   
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> **Iink to info on stis**  
>  _crabs_  
>  http://www.ashasexualhealth.org/stdsstis/crabs/  
>  _Chlamydia and symptoms_  
>  https://www.nhs.uk/conditions/chlamydia/symptoms/  
>  _Why there is no cure for herpes_  
>  https://www.stdcheck.com/blog/herpes-cure-why-there-is-none/  
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> **Links to info about STI's with no symptoms**  
>  _One_  
>  https://www.uwhealth.org/news/dr-jacqueline-gerhart-many-with-herpes-show-no-symptoms/37160  
>  _two_  
>  https://www.plannedparenthood.org/learn/teens/ask-experts/can-you-have-an-std-but-have-no-symptoms-at-all-and-if-so-what-disease-2  
>  _three_  
>  https://www.self.com/story/stds-you-can-have-without-knowing-it  
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> 
> **Additional Links that will help**  
>  _How Often you should get tested_  
>  https://www.prioritystdtesting.com/blog/how-often-should-i-get-tested-for-stds/


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